The invention relates to polarization stabilization, more especially to devices and methods for stabilizing the polarization state of an optical signal of arbitrary, possibly time variant, polarization.
A polarization stabilizer is a device that transforms an input optical beam into an output optical beam with fixed state-of-polarization (SOP) and optical power not dependent on the input SOP. Such a device is useful in coherent optical receivers for matching the SOP between the signal and the local oscillator, in fiber optic interferometric sensors, and in optical systems with polarization sensitive components. A fundamental requirement is the endlessness in control, meaning that the stabilizer must compensate in a continuous way for the variations of input SOP.
Several polarization control schemes based on finite range components have been presented [1-12]. In such schemes, in order to achieve an endless control, it is necessary to provide a reset procedure when a component reaches its range limit so that the output SOP does not change during the reset.
Generally, reset procedures can be problematic in that they are often associated with complex control algorithms designed to avoid loss of feedback control during the reset.